【作者】 崔丽莉；

【导师】 王策；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2011， 博士

【摘要】 本论文选用导电材料为掺杂剂,通过物理复合和化学复合的方法让之与聚合物基质进行复合,希望材料在较低的掺杂量的同时具有较高的介电常数并且具有良好的机械性能,本论文主要有以下三部分组成：(1)为了得到介电性能良好并且相分离现象不明显的复合材料,本部分从分子设计的角度入手,采用氧化偶联的聚合方法,通过化学键连接的方式把导电性能优异的苯胺齐聚物接到聚合物的主链中,分别制备了四种不同链柔性的电活性聚合物,对它们的结构和性质分别进行了研究,探索分子链柔性对介电性能等性能的影响。(2)为了得到介电常数更高的全有机低密度的复合材料,本部分首先采用有机低密度的聚苯胺纳米纤维为掺杂材料让其与聚偏氟乙烯复合；然后为了降低掺杂材料和聚合物之间相分离现象的发生,采用一种“类原位聚合”的方法制备侧链含有聚苯胺的全有机聚合物材料。通过调节两种单体的比例,可以得到一系列具有不同介电常数的聚合物材料。(3)为了降低介电损耗,采用溶液共混的方法制备二氧化钛包覆的多壁碳纳米管／聚偏氟乙烯复合材料,二氧化钛包覆层能起到钝化层的作用,得到了介电常数较高介电损耗较低的导电材料／聚合物复合的介电材料;为了使材料在较低掺杂量的同时具有较高的介电常数,我们采用具有电学性能更加优异、热传导系数高和比表面积大的石墨烯为掺杂材料,采用氧化石墨烯在聚偏氟乙烯溶液中的原位还原的方法制得石墨烯与聚偏氟乙烯的高频下高介电复合材料。更多还原

【Abstract】 High-technology fields require new high-dielectric-permittivity materials. High-technology electronic devices require new high dielectric permittivity materials (known as high-K materials).With the advantages of good mechanical and dielectric performance, composite materials that consist of a flexible polymer loaded with ferroelectric high-K ceramic or conductive fillers have been widely studied, because of their potential applications in some fields such as high charge-storage capacitors, artificial muscles, smart skins, and apparatus used in high-speed integrated circuits. In addition, high-K materials reduce the size of microwave devices, since the wavelength that travels through the medium is inversely proportional to the square root of the permittivity, and it leads to a lower production cost.Even though many ceramic materials that have a high dielectric permittivity and a low dielectric loss are presently used in electronic fields, they are generally brittle in nature, sinter at high temperature, and entail a complicated fabrication process. To overcome these disadvantages, ceramic/polymer composites are better alternatives, However, the dielectric permittivity of the common polymer is extraordinarily low (below 10). Thus, enhancing the dielectric permittivity of the polymer-based materials and keep their mechanical performance of the composites is necessary. Many researchers have been done on ceramic-polymer composite systems that adopt ceramics as fillers, e.g., BaTiO3, CaCuTi4O12, PZT, and PMN-PT. However, these composites have low dielectric permittivity even at a high loading of ceramics (>50 vol%) and the high loading will deteriorate the mechanical properties of the composites such as flexibility.To dissolve the problem of ceramics/polymer composites, much effort has been done recently in the preparation of conductive filler/polymer composite based on the percolation threshold theory. So the MCNT@TiO2 graphene、polyaniline nanofibers、polyaniline and oligoaniline were chosen as conducting fillers to polymer matrix by physical mixing method or chemical bonding way. The work includes three parts.Firstly, for the sake of obtaining outstanding dielectric properties, chemically bonding the filler to the backbone of the polymer matrix is meaningful objective for the improving compatibility between the filler and matrix. Herein, we use an oxidative coupling polymerization approach to introduce the conductive segments of oligoaniline into polymer main chain to prepare a new kind of electroactive alternant copolymer. We synthesize four different polymers with rigidity aromaticity group、crown ether、long flexible chain and polyethylene oxide in the main chain, respectively. The chemical structure of the electroactive copolymer was confirmed by Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance spectra (NMR) spectroscopy measurements. Electrochemical activity of the copolymer are tested in H2SO4 aqueous solution. Moreover, the thermal properties of the copolymer were investigated by thermogravimetric analysis (TGA). With the solubility enhancement of the polymer, the dielectric constant is 6.4,13,58 and 1690 at 1 kHz, respectively.Secondly, due to the high conductivity and low density, polyaniline is chosen as conducting filler to mix with polymer matrix to get a full organic material with high dielectric constant. First, PANI nanofibers are prepared by a rapidly mixed reaction method. PANI nanobibers/PVDF composites are got by solution mixed method. The max constant of composite achieves 359 at 1 MHz with the PANI nanofibers weight percentage of 20%. Then, A novel copolymer of poly (styrene-co-styrenesulfonate) with different content of styrenesulfonate doped PANI (SSPANI) was prepared by free-radical polymerization method. Through adjusting the weight ratio of SSPANI to styrene, SSPANI loading in the copolymer could be well regulated so that a series of copolymers with different dielectric constant were obtained. In contrast to the simple physical mixing approach, the chemical bonding method is an effective way to avoid phase separation. Due to the well dispersion of PANI, the copolymer exhibited a super high dielectric constant compared to common polymer (about 3) and by simple physical mixing method at high frequency at room temperature. When the content of SSPANI reached 35% (wt%) in the copolymer, the dielectric constant of the copolymer was approximately 1300 at 1000 Hz, which was about 400 times larger than that of common polymer. The high dielectric constant behavior originated from the Maxwell-Wagner-Sillars (MWS) theory.Thirdly, for the purpose of reducing dielectric loss, we choose TiO2 coated carbon nanotubes as conducting fillers, and then we prepared MCNT@TiO2/PVDF composites materials by solution mixing method. For the contrast, the TiO2 layer worked as a passivation layer, The TiO2 dielectric shells not only act as interparticle barriers to prevent from direct connection of MCNT, but they also produce excellent compatibility between the fillers and the polymer matrix and ensure the dispersion of fillers in the matrix. The resultant high performance of such new polymer composites makes them particularly attractive for technological applications in flexible high-k components such as the PCB-embedded dielectric components. To get a lower percolation threshold and high dielectric constant material, we fabricate a novel composite with high dielectric permittivity containing PVDF and graphene nanosheet by an in-situ reduction approach. The mono- or a few layers graphene nanosheets were chosen as conductive filler due to their unusual properties, such as fascinating electrical property, high thermal conductivity, good mechanical property and large specific surface area. The graphene/PVDF composite film exhibited a dielectric constant of 148 at percolation threshold of 4.08 vol% at 1000 Hz, which was a lower value. The highest dielectric permittivity of the film with 12.5 vol% of graphene fillers achieved 2080 at 1000 Hz. The dielectric behavior could be endorsed to Maxwell-Wagner-Sillars (MWS) theory at percolation.更多还原